The invention relates generally to a switch cabinet and, more particularly, to a high-frequency-shielded switch cabinet that utilizes electrically and magnetically conductive sealing strips that are high-frequency (HF) impervious.
The manufacture of an HF impervious switch cabinet with a sufficiently long life span is very complicated and expensive. Among the fundamental issue of concern to the manufacturer is whether the switch cabinet features a rack onto which the wall elements and the cabinet door are attached, or whether the wall elements are themselves connected, e.g., welded into a unified cabinet body.
It is well known in the art that switch cabinets can be manufactured of stainless steel, whereby contact strips are applied in the area of the gaps, providing HF imperviousness.
It is also known that a separate, closed insert can be placed in the switch cabinet in order to achieve HF imperviousness, as is illustrated in DE 3611 693 C1. Such additional insert has its drawbacks in that it increases the cost of the switch cabinet by a considerable amount.
A method of manufacturing a sheet metal housing from a housing body having at least one opening is known from DE 91 00 798 U1, in which a switch cabinet having a door, wall element, floor plate, cover plate, flange plate or the like to serve as a closing part for the purpose of closing it, whereby the closing part around the opening of the housing body can be connected to it so as to be electrically and magnetically conductive.
Following manufacture, the body of the housing which is made with sheet metal is provided with a contact surface around the opening. This contact surface is covered by means of a covering band before it is cleaned and then painted. The covering band is finally removed. The contact surface comprised of highly conductive and corrosion resistant material is fused or welded on, for which purpose laser technology is preferably used. This procedure is not only complex, it also requires considerable installations in order to be implemented.
As DE 42 07 308 A1 illustrates, this known method is improved in that the housing body is greased prior to the attachment of the contact surfaces, and the contact surface is attached to the greased housing body around the opening by means of the flame spray method. The contact surface is then covered with the covering band, the housing body is cleaned and then painted. Finally the covering band is removed. In this way the expense for preparation is reduced and the manufacture of the switch cabinet is simplified. The corrosion resistance in the area of the contact surface, however, is insufficient, thus resulting in a decrease in life span and a weakening of the HF shielding.
An object of the invention is to provide an HF impervious switch cabinet that overcomes some of the problems and shortcomings of the prior art.
Another object of the invention is to provide an HF impervious switch cabinet which allows for ease of manufacture while maintaining minimal installation complexity, and still results in an increased life span with a decreased tendency to corrode. How these and other objects are accomplished will become apparent from the following descriptions and from the drawings.
The invention involves wall elements and the cabinet door that are finished with aluminum-zinc coated sheet metal. Such wall elements and door are not provided with any additional surface protection coating, at least not in the areas facing the slots which are to be sealed. Sealing strips are connected directly to the untreated surface of the wall elements and/or cabinet door.
The use of aluminum-zinc coated sheet metal offers the advantage that expensive stainless steel and corrosion susceptible chromed steel sheet can be avoided. The aluminum zinc coated surfaces of the cabinet body can be used without any additional surface protection coating. If an aesthetic adaptation to other switch cabinets is required, then the application of a surface protection coating can remain limited to the outside. The electrically and magnetically conductive sealing strips for HF sealing of the gaps can be directly connected to the untreated inside of the cabinet body.
The improvement in corrosion protection as compared to steel depends on the formation of a solid and adhesive covering layer on the initially used material and on the cathodic protective action of the zinc portion. The abrasion values with respect to bright steel sheet are reduced to fractions, resulting in the advantage of a manifold increase in the life span of the new switch cabinet precisely in the area of the contact points that provide the HF imperviousness.
One embodiment of the new switch cabinet is characterized by the fact that it features a rack finished solely with aluminum-zinc sheet metal (i.e., the rack is not protected with any additional surface protection coating). Wall elements and the cabinet door are attached to the rack with the wall elements being sealed on to the rack through the use of sealing strips. Such embodiment allows the sealing strips to be fixed to the rack or fixed to the wall elements and the cabinet door thereby resulting in a noticeable savings during the manufacture of the rack.
If, for aesthetic reasons, matching is required, then the outer side of the wall elements and the cabinet door can be covered with a coating such as a powder coating or paint. Such coating can be limited to the outer surfaces of the wall elements and the cabinet door.
If additional parts such as flange plates or the like are attached to the cabinet body, then the design is advantageous in that openings in the wall elements of the cabinet body can be closed by means of aluminum-zinc sheet metal finished flange plates or the like. Such plates can be inserted in the known manner into flange plate openings using sealing strips. In such embodiment, the flange plates or the like are not provided with any surface protection coating on the side that faces the inside of the cabinet body and bears the sealing elements. Also, the flange plate openings have no surface protection coating, at least at the contact surfaces that face inward.